Brake Prone to Locking

How do I make the brakes less prone to lockup?

I am new to karting and have an LO206 powered CompKart 4R. It is very difficult to modulate the brakes and very prone to lockup. I had a very experienced racer drive the kart and he concurs that the brakes are prone to lockup. After a few laps he gave up braking and just coasted around. What can I do to change the feeling of the brakes and prevent them from grabbing causing a lockup?


More information. The brake pads are Free Line 10.7594.00 (banana pads) and were glazed. I sanded them against 80 grit then 320 grit on a plate glass surface. They were degreased before and after sanding with brake clean. I cleaned the brake rotor with a red 3M pad and brake clean. The pads had visibly different gaps between them and the rotor. I re-centered the rotor.

What pads should I try and where is a good place to get them. I live in SE Virginia.

Could you move the attachment rod up the pedal to increase the force on the pedal needed to give the same force at the master cylinder?

This, and also see if you can get harder compound brake pads. That’s typically what we do for drivers who have issues with brake modulation or if a kart has particularly sensitive brakes.

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I have found kart brakes are very easy to push down even on harder compounds in comparison to most racing cars I have driven as such I generally do better on modulation with a harder compound.

WD40 on the disc :joy: (i jest. Don’t do that!)

I’d say it’s all in the pads. For example when I first got my CRG, the chief tech advised me to use different pads. The stock CRG orange had a tendency he said to have little brake effect then straight to lock up. The CRG red pads had much better progressive feel. Orange ones went in the bin.

Try some different pads til you find one that works for you

The 4R is well suited to lower powered classes such as the 206. The brakes have a different design than the Covert but should be more than up to the task. I would want to make sure the piston that actuates the pads is working properly along with linkage too. If that is good then try different pads. The OEM pads are pricy but will likely have the best feel. The aftermarket brand Sinter pads work well but in my experience not quite as good as OEM. It is possible the rotor is glazed over and needs to be cleaned with a scotch brite and brake cleaner too.

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A glazed rotor would have the opposite effect OP is describing (if I understand the post correctly). He’s saying they lock up too easily, glazed rotor or pads would make the brakes less sensitive.

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I was reading “difficult to modulate” and thinking he’s applying some brake pressure and nothing is happening, so he has to push the brakes harder and that is when it locks up, giving a “on-off” feel to the brakes. Also, another responder thought perhaps his pads were contaminated with brake fluid or lubricant in which case the disk needs some attention before installing new pads.

Dean can you elaborate?

How old are the pads - are the pads worn ? Is the friction surface parallel to the steel backing plate ? In my karts the pads turn into wedge shape as friction material wears away

With a worn pad - if it isnt straight - the piston cant slide freely in the bore as the wedge makes the piston bind. Situation gets worse if the pads are worn really thin and pistons need to come out a lot

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You understood what I was trying to say. There is an on-off feel to the brakes. This is very dissapointing as I went to the Orland Kart Center for some one on one coaching in a race kart and my only tallent was braking.

The pads were glazed and rough around the edges but fairly parallel. The pad thicknes on one pad varied from 10.25 mm to 10.73mm. There was a small lip on the outside of one pad.

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I would lay a piece of 100 grit sand paper against some level surface, rub the pad in cross hatch pattern so the pad gets flat. Measure and apply pressure to the thickest corner so the pad comes parallel. The finer the grit - the more rounded the result will be - not flat . After you are done - tap the pads against each other so all the dust leave the pores

I usually trim the pad edge, scribe a line where the disc ends and cut excess pad material away. I dont cut in 90´ to backing plate but in an angle. I want to leave as much pad to plate bonding area. Without trimming - the lip will be running on top of the disc and may cause some delay, mismatch, interference before pad finds it spot and actual friction surface takes contact. The lip doesnt have meaninful braking effect. Just rubs the top of the disc and creates heat

When the pads are out, pump the brake pedal so piston comes out a bit, clean the pistons, apply some lube, push them back in and do this for few times. Should remove most of the dust dirt etc without taking the caliper apart

Shim the pads so the pistons are pushed back - deep into caliper body. Leave about 1mm of play on each side. Dont make a tight fit - the brakes will drag if theres not room for expansion, axle bending etc

Rotate the axle and push sand paper agaisnt the brake disk. Move the sand paper in radial direction so it makes somewhat cross hatch pattern

I have seen some GP motorcycle guys reduce the effectiveness of the rear brake - they dont want the rear to lock - by milling a channel to each pad. Depending on pad size - I have seen channels 5-8mm wide. If you want to try - the channel doesnt need to be deep - 1mm is plenty. That reduces the contact surface area. If it doesnt work or make a difference - the pads will be back to normal after using 1mm

One-shot cure for brake glazing: the night before you go to the track, wipe the rotor with a rag soaked in salt water.

The pitting from the rust will be “grabby” for one lap and then the brakes will work perfectly for the life of the pad and rotor.

The design of the 4R caliper is a little different from traditional piston in a caliper design. Its more similar to a wheel cylinder on drum brakes of a car, but the piston actuates two levers to push the pads. I have never worked on one just a visual. Since there are more moving parts make sure nothing is worn or binding.

I was very careful on the brakes today. It didn’t help. Tangled with another kart, who locked his brakes, during the heat race and busted up the LF and steering shaft. If I can find a set of brake pads I will try to mill the pads as suggested above.

When I raced my motorcycle I had rear drum brakes and just didn’t ever use them. I gather that the fast guys now use a thumb lever for rear brakes.

I spoke with someone from J3. They recommended:

  • removing the brake pad shims, I have one per pad
  • positioning the brake pedal to master cylinder rod to reduce the throw